One of the key components of a computer system is a place to store data. Typically computer systems employ a number of storage means to store data for use by a typical computer system. One of the places where a computer can store data is in a disk drive which is also called a direct access storage device.
A disk drive or direct access storage device includes several disks which look similar to 45 rpm records used on a record player or compact disks which are used in a CD player. The disks are stacked on a spindle, much like several 45 rpm records awaiting to be played. In a disk drive, however, the disks are mounted to spindle and spaced apart so that the separate disks do not touch each other.
The surface of each disk is uniform in appearance. However, in actuality, each of the surfaces is divided into portions where data is stored. There are a very high number of tracks situated in concentric circles like rings on a tree. Compact disks have tracks as do the disks in a disk drive. The tracks in either the disk drive or the compact disk essentially replace the grooves in a 45 rpm record. In each drive there are a very high number of tracks. Currently available disk drives have as many as 4000 tracks per inch. Each track in a disk drive is further subdivided into a number of sectors which is essentially just one piece of the track.
Disks in a disk drive are made of a variety of materials. Most commonly, the disks used in rotating magnetic systems is made of a substrate of metal, ceramic, glass or plastic with a very thin magnetizable layer on either side of the substrate. Such a disk is used in magnetic, and magneto-optical storage. Storage of data on a such a disk entails magnetizing portions of the disk in a pattern which reflects the data. Other disks, such as those used in CD's, are plastic. Data, such as songs, is stored using laser to place pits in the media. A laser is used to read the data from the disk.
As mentioned above, to store data on a disk used in a rotating magnetic system, the disk is magnetized. In order to magnetize the surface of a disk, a small ceramic block known as a slider which contains at least one magnetic transducer known as a read/write head is passed over the surface of the disk. These combination read/write heads come in several varieties including ferrite heads, metal in gap ferrite heads and thin film heads. Some ceramic blocks contain a separate read head and a separate write head. The separate read head can be a magnetoresistive head which is also known as an MR head. Each one of these types of heads is sensitive to electrical discharge. The MR head is the most electrically sensitive of the transducers mentioned above.
In addition to being an electrically-sensitive device, a disk drive is a very, very precise piece of mechanical machinery. For example, the ceramic block which holds one of the types of heads discussed above, is flown at a height of approximately six millionths of an inch or less from the surface of the disk and is flown over the track as the transducing head is energized to various states causing the track below to be magnetized to represent the data to be stored. In many disk drives the fly heighth is approximately three millionths of an inch. Some systems now also use near contact recording where the slider essentially rides on molecules of liquid lubricant on the surface of the disk. With near contact recording, the ceramic block passes over the disk within one millionth of an inch or less.
To retrieve data stored on a magnetic disk, the ceramic block or slider containing the transducing head is passed over the disk. The magnetized portions of the disk induce a current in the transducer or read head. By looking at output from the transducer or read head, the data can be reconstructed and then used by the computer system.
Like a record, both sides of a disk are generally used to store data or other information necessary for the operation of the disk drive. Since the disks are held in a stack and are spaced apart from one another, both the top and the bottom surface of each disk in the stack of disks has its own slider and transducing head. This arrangement is comparable to having a stereo that could be ready to play both sides of a record at anytime. Each side would have a stylus which played the particular side of the record.
Disk drives also have something that compares to the tone arm of a stereo record player. The tone arm of a disk drive, termed an actuator arm, holds all the sliders and their associated transducing heads, one head for each surface of each disk supported in a structure that looks like a comb at one end. The structure is also commonly called an E block. A portion of metal, known as a suspension, connects the sliders to the E block. At the other end of the actuator is a coil which makes up a portion of an voice coil motor used to move the actuator. The entire assembly is commonly referred to as an actuator assembly.
Like a tone arm, the actuator arms rotate so that the transducers within the sliders, which are attached to the actuator arm can be moved to locations over various tracks on the disk. In this way, the transducing heads can be used to magnetize the surface of the disk in a pattern representing the data at one of several track locations or used to detect the magnetized pattern on one of the tracks of a disk. Actuators such as the ones described above are common to any type of disk drive whether its magnetic, magneto-optical or optical.
As mentioned above, there are a very large number of tracks per inch on the disk of a disk drive. The actuator is used to very precisely move the transducer to the position over a particular track. Sophisticated electronics are used to keep the actuator over a particular track on a disk. In the industry, this is referred to as track follow servoing. As many as 128 samples are taken on each revolution of the disk to make sure that the transducer is following or tracking a particular track on a disk. Holding the transducer over a particular track while it's rotating at 7200 revolutions per minute can become difficult if vibrations are introduced into the disk drive.
In the past, disk drives were much larger in size and the spacing between the tracks, known in the industry as track spacing, was farther. In the past, large shock absorbing pads were used in an attempt to isolate vibrations and prevent them from causing problems with the disk drive's servoing system. The shock absorbing systems usually include a large rubber grommets on large bolts and came in a variety of arrangements. Presently, as disk drives have become smaller and smaller, the track to track spacing has become closer such that the large shock absorbing systems of the past no longer prevent problems. The large shock absorbing systems of the past transmit vibrations which cause the actuator and slider attached to it to vibrate. Since the transducer is carried by the slider, the vibrations cause the transducer to vibrate back and forth across the track. Errors in reading result since the transducer can not maintain a position over the track where the representations of the data are stored. Its kind of like trying to read a book in an automobile. An adult can read a child's book with large print quite easily in a luxury car, but its impossible to read the fine print at the end of a contract while riding down a bumpy road in a subcompact.
Also, as a practical matter, the shock absorbing systems of the past are too large for today's disk drives. The large shock absorbers are mostly on the 5.25" form factor disk drives. For today's 3.5" disk drives, which are, at most, one-quarter the size of the 5.25" form factor disk drives, the shock absorbers take up too much space. The shock absorbers can not be designed to fit the smaller form factor drives given the space constraints associated with the smaller form factor drive. Simply put, on 3.5" disk drives and smaller form factor disk drives cannot accommodate the shock absorbing systems designed for the much larger drives of the past.
With these smaller form factor disk drives, designers have elected to directly mount the disk drives to the frames of the computer into which the disk drives will be placed. Most of the disk drives include threaded openings which directly receive screws from the frame of the computer system. Another problem has cropped up as a result. When a screw is directly threaded into the housing or frame of a disk drive it causes distortion of the housing. To prevent problems in the operation of the disk drives, the torque or amount of force used to thread the screw into the disk drive must be carefully controlled to limit the distortion caused so problems will not result. The distortions that result are very small in terms of what most people think would result in a problem. However, if these screws are overtorqued slightly the distortion in a metal frame can result in the actuator not properly reading the data on the disk. The distortion will essentially move disks slightly with respect to the actuator.
The amount of torque applied to a screw for mounting a disk drive can probably be controlled somewhat at some manufacturing sites. Some manufacturers are probably sophisticated enough to control the amount of torque or force applied to a screw for mounting a disk drive. However, many other manufacturers of computer systems as well as end-users which buy these disk drives to put into their home systems or business systems merely tighten the screws until they feel it is "snug". What is considered properly "snug" to end users applying torque to a screw will vary. Varying degrees of "snuggness" will result in some problems. Accordingly, there is a need for a method to directly mount the disk drive to a computer system such that the torque applied to a fastener is not as critical and hence will not result in excessive distortion of the disk drive frame.
Another problem is associated with the use of electrically sensitive components within the disk drive. One example of an extremely sensitive electrical component is the magnetoresistive transducing heads that are now becoming more common in the industry. The DC voltage of the housing must be carefully controlled and as a result the disk drive must be mounted to the computer system such that the housing is electrically isolated from the computer system. Consequently, in addition to the need above, there is also a need for a mounting system that will allow the disk drive to be electrically isolated from the computer system into which it is to be mounted.
In short, a disk drive is a very mechanically precise and electrically sensitive device and because the size of the device is consistently becoming smaller and smaller, there is a need for a mounting system or apparatus that will allow direct mounting of the drive to the computer system while electrically isolating that drive from the computer system. There is also a need for a disk drive mounting system that minimizes the distortion on the disk drive despite wide variance in the tightening sequence and amount of torque applied to the screws used to mount the disk drive to the computer system.